The unnamed U.S. officials told NBC News the Israeli attacks were believed to have targeted delivery systems for chemical weapons headed for Hezbollah in Lebanon.
An Israeli spokesman in Washington declined to comment on the specifics of the airstrikes. However, he said, "Israel is determined to prevent the transfer of chemical weapons or other game-changing weaponry by the Syrian regime to terrorists, especially to Hezbollah in Lebanon."
White House officials deferred to the Israelis regarding comment on the attacks.
NBC noted it would be the second time this year Israel tacked inside Syria, the last time coming in January when a convoy of anti-aircraft missiles believed on their way to Hezbollah was destroyed.
Syrian activists charged Friday "dozens" of people had been killed by government troops in a city near the port of Baniyas.
The alleged massacre occurred as the United States and allies examined evidence to determine whether the regime of Syrian President Bashar Assad had used chemical weapons against the rebels.
The main opposition group, the National Coalition, accused the government of a "large-scale massacre" in the town of al-Bayda, the BBC reported.
The group called on the international community "to intervene and put an end to the grievous crimes of the Assad regime."
Rami Abdul Rahman, director of the Syrian Observatory, which monitors human rights violations in Syria, said "dozens of civilians" in the town had gone missing. He said at least 50 people had been "summarily executed, shot to death, stabbed or set on fire."
He said the killings were committed by troops of the Syrian regime and pro-government militiamen.
Syrian troops conducted house-to-house searches in al-Bayda Friday, Abdul Rahman said, and all Internet and telephone services to the town had been cut.
U.S. President Barack Obama said Thursday he was still weighing options on Syria, stressing the need to be thorough in investigating claims Syrian troops used chemical weapons.
During a news conference with Mexican President Enrique Pena Nieto in Mexico City, the president said: "We want to evaluate and make sure that every step we take advances the day Assad is gone. We want to make sure that we look before we leap and that what we're doing is actually helpful."
Defense Secretary Chuck Hagel said the administration was weighing arming the opposition, Politico reported.
"As we've seen evidence of further bloodshed, potential use of chemical weapons ... what I've said is we're going to look at all options," Obama said in Mexico City.
At a news conference Thursday at the Pentagon, Hagel confirmed reports the administration was considering arming Syrian rebels in the wake of the possible use of chemical weapons by the Assad regime but no decisions had been made, The Hill reported.
"You look and rethink all options. It doesn't mean you do, or you will," Hagel said.
British Defense Minister Philip Hammond said during the news conference the West might no longer be able to prove Syria used chemical weapons against its people because evidence samples have degraded.
As a result, Washington and its allies may have to wait for fresh evidence from further attacks before deciding a "red line" had been crossed by the Assad regime that would set off a Western response, Hammond said.
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